MET 112 Global Climate Change - Lecture 6

Wildfire Impacts

Dr. Craig ClementsDr. Craig ClementsSan Jose State UniversitySan Jose State University

Outline Wildfires Aerosols

Del Puerto Canyon Fire California July 2006

Wildland Fire is a Complex Environmental System

wildfire - an unwanted fire that requires measures of control.

prescribed fires - when a fire is used to manage land resources. Prescribed fires can be natural fires that are allowed to burn

under specified conditions or fires that are ignited by resource managers.

flame length –height above ground of flame

black line – Pre-burning of fuels adjacent to a control line before igniting a prescribed burn.

head fire - A fire spreading or set to spread with the wind.

backing fire – A fire spreading or set to spread into (against) the wind.

Fire Terminology

Burn over caused 5 firefighter fatalitiesBurn over caused 5 firefighter fatalities Rate of spread=20-40 mph (10-20 m sRate of spread=20-40 mph (10-20 m s-1-1) ) Flame lengths = 90 feetFlame lengths = 90 feet Convection column of up to 18,000 feet high occurred.Convection column of up to 18,000 feet high occurred.

Esperanza Fire: October 26, 2006Fire Fighter Fatalities

Photo by Tim Becker

Prescribed Fire-

used to maintain ecosystems

(a) (b)

(c) (d)

Infra-red Video Imagery During Ignition

Protecting Resources

What do wildfires emit to the atmosphere?

Stuff like… Ash, Soot (Aerosols) CO2

CO NO and NO2 –precursors for Ozone formation

Atmospheric Aerosols

Microscopic liquid/solid particles– Natural sources - examples:

Volcanoes (sulfur) Fires, dust

– Dust, sulfate particles reflect incoming sunlight: ___________________

– Smoky soot absorb incoming sunlight: ____________________

Cool atmosphereCool atmosphere

warm atmospherewarm atmosphere

Aerosols (II)

Natural sources include:– Dust, sea salt and volcanic emissions

Anthropogenic sources include – Automobiles, factories and biomass burning.

Biomass burning:– Anthropogenic portion: burning of large forests for agriculture

Aerosols have ‘short’ relative lifetimes– They can ‘float’ around for a few days to a week or two.

Aerosols affect the Earth’s energy balance by – reflecting incoming energy and/or – absorbing incoming shortwave and longwave radiation.

Cooling influence is stronger

Aerosols (III)

There are three major types of aerosols

– Sulfate aerosols

– Black carbon aerosols

– Organic carbon aerosols

– All have been increasing in concentration over the last 150 years – the industrial revolution.

Sulfate Aerosols

Natural source: volcanoes Anthropogenic sources: burning of fossil fuels 90% of sulfur aerosols are anthropogenic Example: SO2 (sulfur dioxide-

– From coal combustion Sulfate aerosols increasing globally Sulfate aerosols reflect incoming solar radiation.

Total effect on Earth’s energy budgetTotal effect on Earth’s energy budget

CoolingCooling

Black Carbon (Aerosols)

Natural source:– Natural biomass burning

Anthropogenic source– incomplete combustion from coal and diesel

engines; biomass burning Also know as - ‘Elemental Carbon’ or ‘soot’ Black carbon absorbs solar radiation

– It’s black so has a low albedo. Potentially harmful if inhaled.

Total effect on Earth’s energy budgetTotal effect on Earth’s energy budget– WarmingWarming

Organic Carbon (Aerosols)

Natural source

– Natural biomass burning Anthropogenic source

– Burning fuel

– Biomass burning Produced as a result of incomplete combustion. These aerosols are reflective

Total effect on Earth’s energy budgetTotal effect on Earth’s energy budget

– CoolingCooling

Aerosol Observations from NASA Satellite

What about around the world?

Indirect Effect due to aerosols (I) Certain aerosols may enhance cloud production and

character Recall how clouds form

– Water vapor condenses to liquid water– This processes requires ‘cloud condensation nuclei’– Examples of cloud condensation nuclei

Dust, salt, smoke (all of which are natural aerosols) So, aerosols (with both natural and anthropogenic origin)

– may serve as cloud condensation nuclei.

Indirect Effect due to aerosols (II)

More cloud condensation nuclei– would enhance cloud production

The question then is how would clouds change– Current understanding is that This processes would increase cloud albedoThis processes would increase cloud albedo

This idea of enhanced cloud formation by increases in aerosols is termed – The ‘indirect effect’ of aerosols

Understanding of these processes is currently incomplete.– But model results suggest more low clouds and thus

Total effect on Earth’s energy budget– Cooling– Radiative Forcing: negative– Cirrus cloud (high clouds) production possible, but still uncertain how

important.